The present invention generally relates to coating compositions, including primers for metallic and non-metallic substrates, and topcoats, clear or pigmented.
Difficulties have been encountered in providing durable protective coatings for metallic substrates and the like, such as exterior aircraft components, which are subject to flexing forces and/or which are exposed to adverse environmental conditions such as heat, cold, ultraviolet radiation, high moisture conditions, wind, snow, salt spray, particle impingement, smog, and other harmful environmental factors. The coatings tend to easily peel, chip, blister, or otherwise separate from the substrate, necessitating frequent and costly scraping and recoating operations. Coatings on interior components also deteriorate as a result of exposure to wide humidity changes, abrasions, sudden impacts, and contact with corrosive hydraulic fluids, cleaning fluids, dirt, grime and the like.
Many of the foregoing durability problems can be attributed to the unsatisfactory adhesion of the coating to the substrate surface. On the other hand, difficulties have also been encountered in stripping of coatings, particularly when aged, when non-acid and non-phenolic type strippers are used. As a result, one must often resort to acidic and phenolic strippers which present disposal and corrosion problems.
Accordingly, there has been a need for a coating which can tightly and durably bond to the substrate (and to a top coating, if used as a primer) but which can be readily stripped using standard non-acidic and non-phenolic strippers. The coating must resist peeling, blistering and other separation under adverse conditions, including highly variable humidity conditions. The coating must also remain flexible and resist abrasion and impact and, if necessary, serve as an effective protective coating layer. Such a coating would be useful as a primer or topcoat on any surface exposed to a harsh environment such as the exterior surfaces of aircraft, trains, trucks, ocean vessels, bridges, automobiles and space ships.